Tu C P, Lai H C, Li N Q, Weiss M J, Reddy C C
J Biol Chem. 1984 Aug 10;259(15):9434-9.
Rat liver glutathione S-transferases consist of binary combinations of three major classes of subunits designated as Ya (Mr = 25,600), Yb (Mr = 27,000) and Yc (Mr = 28,000). We have determined the nucleotide sequences of a cDNA insert in pGTR262 containing partial sequence of a Yc subunit. Sequence comparison with a Ya subunit cDNA clone pGTR261 revealed 70% nucleotide sequence homology and 65% amino acid sequence homology in the overlapping coding regions. Approximately 65% of the amino acid substitutions between these two subunits occur in clusters of two to eight residues. The 3' noncoding sequences of these two subunit cDNA clones are highly divergent in length and in sequences. The 3' noncoding region of pGTR262 cDNA contains open reading frames of 23, 39, and 13 amino acids which are in phase with the deduced Yc subunit sequences but interrupted by termination codons. By RNA blot hybridization analysis, we found that this Yc subunit sequence expression is tissue specific. It is expressed at a reduced level in kidney and testis as compared with liver and hardly at all in heart, lung, seminal vesicles, and spleen. We suggest that the mechanism for the tissue-specific expression of the Yc subunit of rat liver glutathione S-transferases may occur at or prior to the level of RNA processing. From the divergent DNA sequences between the Ya and Yc subunits reported in this communication and their differential induction upon acute phenobarbital administration reported by Pickett et al. (Pickett, C.B., Donohue, A. M., Lu, A. Y. H., and Hales, B. F. (1982) Arch. Biochem. Biophys. 215, 539-543) we propose that the Ya and Yc subunits of rat liver glutathione S-transferases are encoded by separate gene families or transcriptional units.
大鼠肝脏谷胱甘肽S-转移酶由三种主要亚基类型的二元组合构成，这些亚基分别命名为Ya（Mr = 25,600）、Yb（Mr = 27,000）和Yc（Mr = 28,000）。我们测定了pGTR262中一个cDNA插入片段的核苷酸序列，该片段包含Yc亚基的部分序列。与Ya亚基cDNA克隆pGTR261的序列比较显示，在重叠编码区域中核苷酸序列同源性为70%，氨基酸序列同源性为65%。这两个亚基之间约65%的氨基酸替换发生在由两到八个残基组成的簇中。这两个亚基cDNA克隆的3'非编码序列在长度和序列上高度不同。pGTR262 cDNA的3'非编码区包含23、39和13个氨基酸的开放阅读框，它们与推导的Yc亚基序列同相，但被终止密码子中断。通过RNA印迹杂交分析，我们发现该Yc亚基序列的表达具有组织特异性。与肝脏相比，它在肾脏和睾丸中的表达水平降低，而在心脏、肺、精囊和脾脏中几乎不表达。我们认为，大鼠肝脏谷胱甘肽S-转移酶Yc亚基组织特异性表达的机制可能发生在RNA加工水平或之前。根据本通讯报道的Ya和Yc亚基之间不同的DNA序列以及Pickett等人（Pickett, C.B., Donohue, A. M., Lu, A. Y. H., and Hales, B. F. (1982) Arch. Biochem. Biophys. 215, 539 - 543）报道的它们在急性给予苯巴比妥后的差异诱导情况，我们提出大鼠肝脏谷胱甘肽S-转移酶的Ya和Yc亚基由不同的基因家族或转录单位编码。
